Attention has been paid to a three-dimensional filaments-linked structure (hereinafter may also be referred to as 3DF) in which thermoplastic resin fibers in molten states (molten filaments) are linked in a three-dimensional steric net shape, and the three-dimensional filaments-linked structure is used as a core material (a core) of a mattress overlay (mattress pad) which is placed on a top of a conventional mattress, futon, or the like to improve sleep environment more comfortable.
This three-dimensional filaments-linked structure is acquired by extruding a thermoplastic resin material such as polyethylene or polypropylene in shapes of continuous lines (the filaments) from an extruder via plural nozzles, tangling and linking (fusing) these filaments in the three-dimensional net shape, and promptly cooling these filaments in such a state.
The applicant has proposed a manufacturing method of an antidecubitus mattress (see Patent Literature 1 and the like), and in the method, by changing a transfer speed of an endless conveyor which receives the three-dimensional filaments-linked structure immediately after formation of the three-dimensional net, filament density (hardness of the mattress core material) is changed per region (block) at plural stages at an arbitrary position along a longitudinal direction (a height direction) of a sleeper's body.